1. Field of the Invention
The present invention relates in general to resilient support columns for height-adjustable chairs, tables and the like, of the type including a pneumatic spring as the operating component, and pertains in particular to a novel retention system for facilitating the installation and removal of pneumatic spring operators in such columns.
2. The Prior Art
In one type of known adjustable-height support column, the column includes two telescopically movable tubular members, one being attached to the surface to be supported, e.g. a chair seat, and the other being attached to the supporting structure for the surface, e.g. the base of a chair. A piston-and-cylinder type pneumatic spring, containing a gas or gas/oil mixture under high pressure, is inserted within the two tubular members, with the piston rod member being operatively connected in load-transmitting relation to one of the tubular members and the cylinder member being similarly connected to the other tubular member. The overall length of the pneumatic spring, and thus the height of the support column, may be adjusted by operation of a manually-operable valve mechanism internal to the spring.
In the assembly of such prior art support columns, the pneumatic spring is typically inserted axially into one of the tubular members, e.g. the upper member connected to the surface to be supported, and then retained therein by a spring clip, plugs, ball detents, etc., acting between the tubular member and the cylinder of the pneumatic spring. For example, such a prior art support column is described in U.S. Pat. No. 3,788,587, issued Jan. 29, 1974 to the assignee of the present application.
Although these prior art retention systems do to some extent facilitate assembly and disassembly of the pneumatic spring, they have not been altogether satisfactory in that they require special-purpose retention devices or structures, e.g. ball detents, retention grooves, and the like, in the cylinder member of the pneumatic spring itself. Also, the spring clips, plugs, etc. used to fasten the pneumatic spring to the column are external, non-attached parts that are subject to being lost and working loose during use. Moreover, these external devices necessitate a secondary installation step after the pneumatic spring has been inserted in the tubular column which is time consuming and ofttimes difficult to carry out properly. A further disadvantage of the prior art retention mechanisms is that they do not assure a firm engagement between the load-transmitting surfaces of the pneumatic spring and the tubular members of the column, nor do they provide the desired close fit between the valve-operating components of the pneumatic height-adjustment system. If too great a clearance is permitted among these respective bearing surfaces and components, it can interfere with the proper operation of the valve operator for the pneumatic spring and additionally could produce undesired chatter during use or adjustment of the chair.